Arithmetic and logic operations belong to the basic operations of information processors. The preferred operations are additions and subtractions and the logic functions AND, OR and XOR. Known processors contain an arithmetic and logic unit which comprises a binary adder unit and a separate logic unit for performing logic functions (FIG. 1). The design of arithmetic and logic units in integrated circuits is disclosed by Rabaey, "Digital Integrated Circuits, A Design Perspective", published by Prentice Hall, Englewood Cliffs, U.S.A., 1996, pages 383-408.
The known adder and logic units are also used to perform special functions such as processing character strings of variable length as required by database and text processing applications. DE 43 34 294 discloses a device of this type which includes an adder unit, a logic unit and an additional compare unit each of these units having its own operand input and output lines. With the increase of the circuit density wiring and wire delay becomes more and more a serious problem. The large number of input and output lines increase the RC delays and the capacity of the wiring and thus reduces the operation speed of the processor. In addition, the input lines represent a large fan-in characteristic which also reduces the timing of the circuits.